AbsoluteTelnet told me that there was a newer version available. So, I downloaded and installed it thinking that it was a free upgrade. But, I guess it is going to cost $19.95 to upgrade. I really don't need to upgrade to the newer version. So, I would like to uninstall 3.50 and go back to the previous version. Where can I download 3.1x?

You can still download old versions using the same kind of link. The only thing is that version 2 and version 3 are no longer available on the website. Just substitute any version you need (other than 2.xx or 3.xx) in the link and you can download that version.